Extending the window for acute stroke treatment: thrombolytics plus CNS protective therapies

Experimental Neurology 188 (2004) 195 – 199 www.elsevier.com/locate/yexnr

Commentary

Extending the window for acute stroke treatment: $ thrombolytics plus CNS protective therapies Kenneth R. Wagner a,b,* and Edward C. Jauch c a Department of Neurology, University of Cincinnati College of Medicine, Cincinnati, OH 45267, USA Medical Research Service, Department of Veterans Affairs Medical Center, Cincinnati, OH 45220, USA c Department of Emergency Medicine, University of Cincinnati College of Medicine, Cincinnati, OH 45267, USA b

Accepted 5 May 2004 Available online 15 June 2004

Introduction. More than 700,000 new strokes occur in the United States each year. Of these, about 80% are ischemic, that is, the result of an intra-arterial blood clot. Without treatment, 36% of patients will remain moderately or severely disabled at 3 months (Marler and Goldstein, 2004). The FDA-approved therapy for clot thrombolysis in ischemic stroke, recombinant tissue plasminogen activator (rt-PA), when administered intravenously within the first 3 h, significantly improves patient outcome by approximately 30% (NINDS rt-PA Stroke Study Group, 1995). Furthermore, a recent pooled analysis of the three randomized rt-PA clinical trials has demonstrated that the earlier rt-PA is administered, the better the outcome with odds ratios of 2.8 and 1.5 for patient treatment within 0– 90 and 91 –180 min of onset, respectively (Hacke et al., 2004). Thus, findings from these 2775 patients demonstrate that early recanalization by thrombolytic therapy clearly improves outcome in acute stroke. Despite these data, the American Heart Association has estimated that while 400,000 stroke patients annually could benefit from tPA administration, only 6000 or 1.5% of patients are actually treated (Mitka, 2003; Marler and Goldstein, 2004). The reasons for this discrepancy are complex, but the main obstacles include the limited 3h treatment window (Kleindorfer et al., 2004) and the potential for rt-PA induced intracerebral hemorrhage (ICH). rt-PA administration to stroke patients is not innocuous, it increases symptomatic ICH rates by 10-fold (0.6% in controls to 6.4% in rt-PA-treated patients; NINDS rt-PA Stroke Study Group, 1995). Furthermore, in the European $

doi of original article: 10.1016/j.expneurol.2004.02.005. * Corresponding author. Medical Research Service, Department of Veterans Affairs Medical Center, 3200 Vine Street, Cincinnati, OH 45220. Fax: +1-513-475-6415. E-mail address: [email protected] (K.R. Wagner). 0014-4886/$ - see front matter D 2004 Elsevier Inc. All rights reserved. doi:10.1016/j.expneurol.2004.05.006

rt-PA trial in which the treatment window was extended to 6 h, the overall symptomatic ICH rate was further increased to 8.4% (Hacke et al., 1998). This risk of symptomatic ICH with rt-PA has raised concerns, especially among emergency physicians in nonacademic community hospitals, who remain uneasy about administering the drug without neurological support (Mitka, 2003). This debate has been highlighted in a recent position paper from the Society for Academic Emergency Medicine (SAEM) (Adams and Chisholm, 2003; Yealy and Adams, 2004) and in a response by Jauch writing for the Neurological Emergencies Interest Group of the SAEM (Jauch, 2004). Undoubtedly, the development of therapeutic approaches for recanalization that have limited risk would engage the emergency medicine community to become more active in acute stroke treatment. Thus, the best direction for future acute stroke therapy development may be to combine a thrombolytic that would enable recanalization with a CNS protective therapy that would reduce the risk of ICH while increasing the treatment window beyond 3 h. It is in this context that the report by Lapchak et al. (2004) in the current issue of Experimental Neurology is of considerable interest. These workers have tested the feasibility and effectiveness of a third generation thrombolytic, tenecteplase (TNK), in combination with a free radical scavenger, the spin trap agent, NXY-059 (Cerovive, Astra Zeneca), in their rabbit small blood clot embolization model of ischemic stroke. In this study, they examined the 1- to 6-h treatment windows for each agent individually and in combination using their quantal-dose response data analysis technique (Zivin and Waud, 1992). In this method, the P50 value, that is, the weight of clot that produces behavioral deficits in 50% of subjects, is determined. The effectiveness of a treatment is then measured by its ability to shift the P50 value to a higher value, that is, a greater

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dose of clot is necessary in the presence of the treatment. Thus, by examining neurobehavioral outcome at 24 h, this blood clot model quantitatively tests the thrombolytic ability of TNK and the neuroprotection of NXY-059. The benefit of combination therapy was observed with the administration of NXY-059 with TNK resulting in additional behavioral improvement compared to either drug alone. Most importantly, delaying the combined drug administration to 6 h post-embolization produced a statistically significant reduction of behavioral deficits. At this later time point, neither drug alone was effective. Thus, these preclinical findings demonstrate that combining a thrombolytic with neuroprotective drug therapy can extend the treatment window for acute stroke in an experimental model as long as 6 h. It is noted, however, that this report did not describe the rate of hemorrhagic infarct conversion with combination treatment. Thus, it will be important in future preclinical studies to define the safety profile of the combination TNK plus NXY-059 therapy. Tenecteplase. Tenecteplase (TNK) is a third generation derivative of human rt-PA with 14-fold greater fibrin specificity, an 8-fold slower plasma clearance, and a 200fold greater resistance to inactivation by plasminogen activator inhibitor-1 compared to rt-PA (Nordt and Bode, 2003; Thomas et al., 1994; Verstraete, 2000). Thus, TNK can be administered as a rapid 5- to 10-s bolus. In contrast, rt-PA requires a 90-min infusion to achieve the same level of circulating drug levels. TNK’s efficacy has been demonstrated in acute myocardial infarction in a phase I doseranging trial, a nonblinded phase II comparison with alteplase and a landmark randomized double-blind phase III comparison with alteplase in 16,949 patients (Nordt and Bode, 2003, review). ICH rates in these trials were among the lowest reported in clinical trials of thrombolytics for acute myocardial infarction (Gibson and Marble, 2001). In the rabbit and rat embolic stroke models, comparison of the pharmacology and dose –response or therapeutic window for TNK with rt-PA have demonstrated a better pharmacological profile for TNK and a similar rate of ICH as rt-PA (Chapman et al., 2001; Zhang et al., 2000). TNK has been recently been studied in a pilot open-label dose escalation study in 75 patients who received TNK within 3 h from symptom onset (25 per 3 dose tiers) (Lyden, 2003). Although no symptomatic ICHs occurred within 36 h of treatment, the dose escalation component of the study did demonstrate that asymptomatic hemorrhages were present on CT-scans in 2/25 and 8/25 in the first two dose tiers. Further testing of the safety and efficacy of TNK is currently being examined in a phase II clinical trial. The findings from this phase II and a future phase III trial of TNK will be important in determining whether TNK receives approval for acute stroke treatment. Oxidative stress in stroke: protection by nitrone spin trap agents. Considerable evidence implicates oxidative stress in secondary pathochemical events following ischemic and hemorrhagic stroke and traumatic brain injury (Chan, 2001;

Wang and Lo, 2003; Wagner et al., 2003; Zheng et al., 2003). Various molecules including proteins, lipids, and DNA are important targets for reactive oxygen species (ROS) that can be generated by metal-catalyzed reactions (e.g., pro-oxidant iron) (McCord, 1998; Wagner et al., 2003). For proteins, metal-catalyzed reactions with hydrogen peroxide that generate hydroxyl radicals can preferentially attack amino acid residues at metal binding site altering their enzymatic activity and increase their susceptibility to proteolysis (Stadtman, 2001; Stadtman and Berlett, 1998). Nitrone-derived spin trap agents were originally developed to study the extremely rapid chemistry of free radical reactions (Green et al., 2003). Spin trap nitrones react with and stabilize free radicals thereby inactivating and preventing their reactions in cellular injury processes. The pharmacological actions of nitrones are numerous as recently outlined by Green et al. (2003). Importantly, nitrones have been demonstrated to be effective neuroprotective agents in various stroke models. The prototype nitrone, alpha-phenylN-tert-butylnitrone (PBN), was first demonstrated in 1990s by several groups to reduce mortality, infarct size, and edema in global and focal ischemia models (references in Green et al., 2003). PBN also improves biochemical measures of outcome in brain injury models (Hensley et al., 1997; Lapchak and Araujo, 2001). PBN reduces tPA-induced hemorrhage, infarction, and neurological deficits in an embolic focal ischemia model (Asahi et al., 2000), decreases the hemorrhage rate in a rabbit model of focal embolic stroke (Lapchak et al., 2001), and improves neurological outcome following ICH in rats (Peeling et al., 1998). In this regard, we have observed that cerebral white matter tissue and the enzyme, creatine kinase, are highly susceptible to ironcatalyzed protein carbonyl formation, and that PBN can effectively reduce the oxidative stress that develops in perihematomal edematous white matter in our porcine ICH model (Hall et al., 1998, 2000; Wagner and Broderick, 2001; Wagner et al., 1996, 2002). The recently developed nitrone free radical trapping agent, disodium 2,4-disulfophenyl-N-tert-butylnitrone (NXY-059), has been demonstrated by Lapchak and Araujo (2003), Lapchak et al. (2002a,b), and by other laboratories to be neuroprotective in several cerebral ischemia models (Green et al., 2003; Kuroda et al., 1999). Interestingly, in a primate model of permanent focal ischemia, NXY-059 improves neurological function and reduces infarct volume even when administration is delayed until 4 h postocclusion (Marshall et al., 2001, 2003a,b). The tolerability and safety of NXY-059 has been studied in two clinical trials in human stroke patients. In two wellconducted, published, phase I and II studies, stroke patients were entered into randomized, double-blind, placebo-controlled, parallel group, multicenter trials that evaluated the safety and tolerability of NXY-059 dosing regimens compared with placebo within 24 h of acute stroke (Lees et al., 2001, 2003). The results demonstrated that NXY-059 was well tolerated in acute stroke even at higher concentrations,

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above those that are neuroprotective in a permanent focal ischemia animal model. NXY-059 is currently undergoing a phase III, 150 site multicountry study with the acronym SAINT (Stroke-Acute Ischemic-NXY-059-Treatment). The goal is to enroll 3000 patients within 6 h of stroke onset. Patients will receive a 72-h treatment regimen of NXY-059 (1 h loading dose following by 71 h of infusion; NIH Clinical Trials at , http://www.ClinicalTrials.gov; The Internet Stroke Center at , www.strokecenter.org). This phase III trial was well-designed in that it considers the acute time window for effective stroke treatment (V6 h) and is employing drug concentrations that are effective in experimental cerebral ischemic models. It is noteworthy that newer potentially more effective nitrones are being developed and studied in cerebral ischemic stroke models. Stilbazulenyl nitrone (STAZN) is a novel second-generation azulenyl nitrone with significantly enhanced potency as a chain-breaking antioxidant versus conventional alpha-phenyl nitrones (Becker et al., 2002). In vitro assays demonstrate that STAZN is about 300 times more potent in inhibiting the free radical-mediated aerobic peroxidation of cumene than is PBN and NXY-059 (Becker et al., 2002). The antioxidant efficacy of STAZN is believed to be unprecedented among archetypal alpha-phenyl nitrone spin traps and rivals the antioxidant potency of vitamin E in a polar medium (Becker et al., 2002). Ginsberg et al. (2003) recently reported their comprehensive and carefully conducted study of STAZN treatment in a rat focal ischemia model of MCA suture occlusion. Various dose regiments of STAZN were examined beginning at reperfusion (2 h postMCA occlusion). Mean cortical infarct volumes were reduced by 64 – 97% and total infarct volumes by 42– 72% at 72 h with STAZN treatment. In over one-half of STAZNtreated animals, cortical infarction was virtually abolished. Hypothermia and other neuroprotective approaches for acute stroke treatment. The future of acute stroke treatment will likely utilize thrombolytic drugs for recanalization and hypothermia and/or a single drug or a drug cocktail to provide CNS protection. Hypothermia has a long history of study and is considered by many to be the most robust of all therapies for brain insults. Even mild hypothermia (33 – 35jC) delivered post-insult has proven to be effective in cerebral ischemia treatment (Dietrich and Kuluz, 2003; Ginsberg, 2003; Ginsberg et al., 1992). In this regard, we have recently found that delayed local brain cooling initiated 3 h after ICH can reduce vasogenic edema development by 50% (Wagner and Zuccarello, in press). Thus, hypothermia as a component of combination treatments may be the most fruitful approach for future stroke treatment since it can affect multiple mechanisms underlying CNS injury. Interestingly, several recent combination trials of drug therapy plus hypothermia in experimental cerebral ischemia have provided significant results. Aronowski et al. (2003) have demonstrated that hypothermia acted synergistically when combined with caffeinol (the combination of caffeine and alcohol) to reduce infarct size by a remarkable 75%.

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Clinically, an ongoing phase I trial of patients receiving thrombolytics combined with hypothermia and a future clinical trial of caffeinol plus hypothermia for acute stroke patients are being conducted at the University of Texas Medical School at Houston by Dr. James Grotta et al. Additional studies that have demonstrated the effectiveness of hypothermia plus drug therapy in experimental cerebral ischemia include post-ischemic moderate hypothermia (30jC) combined with the spin trap agent, PBN (Pazos et al., 1999), the combination of magnesium, antioxidant, tirilazad, and moderate hypothermia (Zausinger et al., 2003), and the combination of hypothermia (33jC) plus BDNF (Berger et al., 2004). Conclusions. The findings from Lapchak et al. (2004) in this issue as well as those of other laboratories have demonstrated the significance of free radical generation during reperfusion following cerebral ischemia and the effectiveness of nitrone spin traps in experimental stroke treatment. Similarly, considerable data indicate that hypothermia alone or in combination with drug therapies is also a powerful treatment approach for CNS protection. Overall, these results strongly support the argument that CNS protective drugs and/or hypothermia should be components with thrombolytics of future acute stroke treatment ‘‘cocktails’’. As described by Zivin (1999) in his review and commentary on the future of acute stroke treatment, recanalization is essential for any combined therapy to enable neuroprotective drugs to penetrate into the ischemic tissue. Importantly, the findings of Lapchak et al. (2004) in this issue demonstrate that combined therapy not only can improve outcome, but also can even extend the treatment window beyond 3 – 6 h post-occlusion. Thus, it is hoped that the ongoing clinical trials of thrombolytics combined with CNS protective therapies that have been carefully designed and based on important findings from experimental results will someday provide effective and safe treatments for acute stroke patients.

Acknowledgments The experimental ICH studies from our laboratory that were referred to in the manuscript were supported by NIH grant R01-NS30652 and funds from the Office of Research and Development, Medical Research Service, Department of Veterans Affairs.

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